Field of the Invention
The invention pertains to apparatus and methods for monitoring the vital signs of a patient. More specifically, the invention pertains to a non-contacting video-based analysis system to monitor vital signs such as respiration.
Description of Related Art
Respiration rate is an important vital sign. Manual methods of determining respiration rate are intermittent and have proven to be unreliable. Continuous methods have limitations; either they are not accurate or are poorly tolerated by patients. Respiration rate is a key indicator of ventilation. Abnormal respiration rate, either too high (tachypnea), too low (bradypnea), or absent (apnea), is a sensitive indicator of physiologic distress that requires immediate clinical intervention.
The most common method for respiration rate measurement is by physical assessment, either by counting chest wall movements or by auscultation of breath sounds with a stethoscope. Many studies have shown manual methods to be unreliable in acute care settings, especially on the general care floor, where the majority of patients receive care. Even if they were reliable, manual methods are limited by their intermittent nature.
Two continuous methods for respiration rate monitoring are used in multiparameter monitors, viz., thoracic impedance pneumography and capnography monitoring.
The thoracic chest wall expands and contracts during the respiratory cycle from which respiration rate can be determined by measuring changes in electrical impedance associated with this movement. Monitoring of respiration rate by thoracic impedance is convenient if the patient is already monitored for ECG, but the method is prone to inaccurate readings due to a number of factors including: ECG electrode placement, motion artifacts, and physiologic events non-related to respiration rate that cause chest wall movement (e.g. coughing, eating, vocalization, crying).
Continuous end tidal CO2 monitoring with capnography is the standard of care in surgical settings to establish end tracheal intubation. Since intubated patients have a clear respiratory pattern without entrainment of room air, it is easy for the capnometer to report the respiration rate. However, capnometers that continuously monitor ventilation for non-intubated patients require a nasal airway cannula that draws a continuous gas sample for spectrographic measurements within the capnometer. Capnometry measurement of respiration rate is the most frequent method used by anesthesiologists. This method is sensitive to central, obstructive, and mixed apneas. The primary limitations of continuous respiration rate monitoring by capnometry are low patient tolerance of the nasal cannula and the added nursing workload to respond to dislodged or clogged cannulas during the patient stay. In addition, any entrainment of room air by the sampling cannula can cause erroneous end-tidal values. A recent study of pediatric patients showed premature cannula dislodgement in 14 out of the 16 patients enrolled in the study.
There is a clear demand for improved methods for respiration monitoring: For general baby monitors, no reliable product exists that can measure respiration without a pad under the bed/child or attachment on the child's diaper or clothing. Reliable monitors are needed, in particular, to address the so-called Sudden Infant Death Syndrome (SIDS). According to the CDC, every year in the U.S., more than 4,500 infants die suddenly of no obvious cause. A significant portion of these deaths are sleep related, where a perfectly healthy baby simply stops breathing in his/her sleep without warning. Other sleep related disorders affect large numbers of people. For example, more than 15% of adolescents complain of some form of sleep problems, many of which may contribute to misdiagnosis of ADHD and other behavioral problems.
Improved monitoring is needed in the hospital environment as well. In spite of its clinical importance, respiration rate is the last core vital sign without a reliable and continuous monitoring solution that patients can easily tolerate. The lack of a reliable respiration rate measurement is a major contributor to avoidable adverse events. One retrospective study of over 14,000 cardiopulmonary arrests in acute care hospitals showed 44% were of respiratory origin. Another study reported that respiratory failure, a key Patient Safety Indicator (PSI), has increased in U.S. Acute Care Hospitals. The reported incidence is 17.4 per 1,000 hospital admissions, leading to over 15,000 avoidable deaths at a cost to the healthcare system of over $1.8 billion.